Kiln

A pottery kiln was a clay-built oven, often partly sunk in the ground, in which vessels were stacked and fired with wood. In 12th-century England potters made cooking pots, jugs, pitchers and bowls; at Stamford, a centre producing from the 9th to the 13th century, potters brushed on distinctive lead glazes in pale yellow, orange, green and blue. Kilns have been excavated at Stamford and, for Stamford-type ware, at Pontefract.

Sources: en.wikipedia.org